Supporting track and advancing pawls for article display and storage apparatus



June 25, 1968 w. B. LYON 3,389,894

SUPPORTING TRACK AND ADVANCING PAWLS FOR ARTICLE DISPLAY AND STORAGEAPPARATUS 5 Sheets-Sheet 1 Filed Oct. 28, 1966 INVENTOR. W////0m 5. L700ATTORNEY 3 Sheets-Sheet 2 7 W. B. LYON SUPPORTING TRACK AND ADVANCINGPAWLS FOR ARTICLE DISPLAY AND STORAGE APPARATUS June 25, 1968 Filed Oct.28, 1966 ATTORNEY June 25, 1968 w. B. LYON 3,389,804

SUPPORTING TRACK AND ADVANCING PAWLS FOR ARTICLE DISPLAY AND STORAGEAPPARATUS Filed Oct. 28, 1966 5 Sheets-Sheet 7 2 25 6 66 52 Ff/ K! m l IH L III I] a 2 W a? 66 22 2a 66 jjg fi INVENTOR.

VIM/mm B. 170/? ATTORNEY BY A United States Patent 3,389,804 SUPPORTINGTRACK AND ADVANCING PAWLS FOR ARTICLE DISPLAY AND STORAGE APPARATUSWilliam Bronson Lyon, 6204 Charlotte Pike, Nashville, Tenn. 37209 FiledOct. 28, 1966, Ser. No. 590,381 7 Claims. (Cl. 211-15) This inventionrelates to improvements in supporting track and advancing pawls forarticle display and storage apparatus. The invention is an improvementof the apparatus disclosed and claimed in Patent No. 2,836,303. Theprincipal objects of the invention are:

First, to provide a track and coacting conveyor and pawls for advancingarticle supporting bars around a generally rectangular circuit withvertical front and back reaches, in which the bar supporting pawls aresupported along both of their sides, and connected centrally to the pawladvancing conveyor chain, so that the weight of articles supported onthe bars does not impart any twisting stress to the conveyor chain orthe connections between the pawls and the chains.

Second, to provide a pawl and chain supporting track with a novelpivotal connection between the pawls and the chain, and a novelarrangement of pawl receiving slots in the track system that permits barsupporting pawls to swing out of bar engaging position at preselectedposi tions along the track in order to pass article supporting bars in apredetermined sequence.

Other objects and advantages of the invention will be apparent from aconsideration of the following description and claims. The drawings, ofwhich there are three sheets, illustrate a practical form of theinvention.

FIGURE 1 is a fragmentary inside elevational view of the supportingtrack and pawl conveyor for supporting and advancing one end of articlesupporting bars between article storage and article display positions,the bars and a drive for the conveyor being shown in section.

FIGURE 2 is a fragmentary vertical cross sectional view along the line22 in FIGURE 1, but with the pawls advanced to the article support bar.

FIGURE 3 is a fragmentary vertical cross sec ional view taken along theplane of the line 3-3 in FIGURE 1, but with the pawls advanced to showthe top pair in FIGURE 1 at the bottom.

FIGURE 4 is a fragmentary horizontal cross sectional view along theplane of the line 44 in FIGURE 1.

FIGURE 5 is a view taken along the plane of the line 5-5 in FIGURE 1,showing the top rail in plan.

FIGURE 6 is a fragmentary vertical cross sectional view taken along theplane of the line 66 in FIGURE 2.

FIGURE 7 is a fragmentary vertical cross sectional view through thebottom rail, on the plane of the line 77 in FIGURE 3, with the pawlsadvanced to the rear.

FIGURE 8 is a fragmentary plan view of the top rail.

FIGURE 9 is a fragmentary plan view of the bottom rail.

FIGURE 10 is a sectional view on line 10-10 in FIG- URE 1, looking up atthe lower set of pawls.

The above identified Patent No. 2,836,303 discloses a cabinet withsupporting and guiding rails in each end for supporting three articlesupport rods for advancing motion through a generally rectangularcircuit within the cabinet. The rods are supported and advanced in theircircuit by two conveyors, associated one wih each guide rail system ateach end of the cabinet. Each conveyor includes two pairs of a leadingpawl and a trailing pawl connected in equally spaced positions along thechain. The two conveyor chains are driven simultaneously by a crossshaft to advance the article support bars between four positions locatedgenerally at the four corners of the cabinet. Thus there is always avacant position around the circuit which is not occupied by a supportbar. This permits articles of considerable length, such as garments onhangers, to hang freely at a forward display position and at twovertically displaced storage positions; and permits the articles on eachbar to be advanced around the storage and display circuit withoutinterference between each group of articles. The leading pawl of eachpair of pawls on the chains must by-pass a support bar to be in positionto support the bar in downward motion to the display position. Thetrailing pawl of each pair must by-pass support bars in some positionsto be able to advance to bars in other positions, and must further beable to tilt out of bar engaging position to leave a bar in one positionand pass on the next bar.

The arrangement of the bar positions, and the sequence of operation ofthe pawls on the conveyor chains is fully described in the patentidentified and so is not disclosed in greater detail. Similarly, thearrangement of two simultaneously operated conveyors is fully disclosed,so the drawings herein illustrate only one conveyor, and supporting andguiding track and rail system. It will be appreciated that the structureillustrated is duplicated in symmetrical relation at the opposite end ofthe storage and display space. The apparatus may be enclosed in asuitable cabinet (not illustrated), or may be built into unused portionsof a building.

The supporting and guiding track system includes a front supporting bar1 and a rear support bar 2. The bars may be suspended from a suitablesupport above or extended downwardly to a lower support (notillustrated). The front and rear bars are of angle shaped cross sectionhaving laterally extending guide flanges 3 and 4 respectively. Thesupport bars are connected by a top cross strap 5 and a bottom crossstrap 6 to provide a rigid rectangular frame. In addition, the straps Sand 6 may be secured to a wall 7 by screws 8 for additional support ofthe frame if desired.

Connected to the top strap 5 is a top support rail 9 of folded metal.Connected to the bottom strap 6 is a bottom support rail 10, also offolded metal. The top and bottom rails 9 and 10 are further connected bya front hanger strap or bar 11 and a rear hanger strap or bar 12. Thefront hanger bar 11 has an angled front guide rail 13 secured thereto asby rivets 14, while a rear angled guide rail 15 is secured to the rearhanger strap as by rivets 16. The direction of travel of the conveyoraround the rectangularly arranged rails is counterclockwise as viewed inFIGURE 1 and as indicated by the arrows. A drive shaft for connectingthe conveyors at each end of the apparatus is indicated at 17 withsuitable journals in the bottom guide rails.

The top guide rail 9 is shown more clearly in FIG- URES 2, 6 and 8 andconsists of an upright flange 18 having a forwardly or inwardly turnedroller supporting fian e 19 intermediate of its height. Below the rollersupporting flange the rail is inclined laterally outwardly as at 20 to alower portion 21 which is secured to the previously described hangerstraps 11 and 12. The lower edge of the lower portion 21 is turnedlaterally inwardly in a broad conveyor supporting rail 22 having a chainsupporting rib 23 secured to its upper side as by screws 24.

The lower guide and support rail 10 has a flat upright side portion 25with a laterally inwardly turned roller supporting track 26 formed near.its lower end. Theinner edge of the roller supporting track is foldeddownwardly and outwardly in an inclined position as at 27 to a lowerconnected edge 28 which is secured to the hanger straps 11 and 12. Abroad conveyor supporting and guiding rail 29 is turned laterallyinwardly from the upper edge of the rail and has a conveyor chainguiding track 30 secured to its lower side as by screws 31.

The front guide rail 13 is of angled cross section and has a laterallyinwardly projecting conveyor guiding flange 32 with a chain guidingtrack 33 secured to its outer edge. The ends of the guiding flange 32 ofthe front rail 13 are connected to the forward ends of the upper andlower rails by curving portions of the flange 32 rearwardly as at 34 and35. Lapped connecting plates or clips 36 secure the ends of the curvedflanges to the lateral flanges of the adjacent top and bottom rails.

The rear guide rail has a laterally turned supporting flange 37 with achain supporting track 38 secured to its rear surface. The ends of theflange 37 are bent into curved corner connecting plates 39 to connectthe upper end of the rear rail to the lateral flang 24 of the top railand to connect the rear end of the lower rail to the lower end of theflange 37. Connecting clips 40 overlap and connect the abutting edges ofthe corner plates and the rails.

Supported at each corner of the rectangularly arranged guide rails is ashaft 41. The shaft 41 at the upper front corner supports a sprocket 42and a sprocket 43 is supported at the junction of the lower end of thefront guide rail and the front end of the bottom guide rail.Corresponding sprockets 44 and 45 are supported at the rear end of thebottom rail and the upper end of the rear rail. A link chain loop 46 istrained around the sprockets 42 to 45 and one of the sprockets is drivenfrom the cross shaft 17 by a connection not illustrated. The severalreaches of the chain loop 46 are supported by the chain supportingtracks 23, 30, 33 and 38 between the sprockets.

The roller supporting track 19 on the upper guide rail 9 is positionedabove the chain supporting flange and is positioned laterally outwardlyto support the rollers 47 mounted on the ends of three articlesupporting bars 48, 49 and 50. The upper roller supporting track 19 hasa forward depression or detent 51 and a rear depression or detent 52 forarresting the motion of the rollers at these points as will bedescribed. In reference to FIGURES 2 and 4 it will be seen that theroller supporting track 19 is positioned behind the laterally turnedflanges 3 and 4 on the front and rear support bars 1 and 2.

The laterally projecting roller supporting track 26 on the lower railhas a similar forward detent or depression 53 and rear depression ordetent 54 and the track 26 is positioned in the plane of the flanges 3and 4 of the support bars. The front hanger support bar 1 has the lowerend of its flange 3 separated and bent inwardly as at 55 to form acontinuous track with the front end of the track flange 26 and theflange 4 of the rear support bar to the lower roller supporting track issimilarly curved at 56.

The article support bars 48, 49 and 50 are advanced around the circuitof the supporting and guiding rails and tracks by two pairs of leadingand trailing pawls indicated generally at 57A and B in FIGURE 1 andconnected to the chain loop 46 at diametrically opposite or equallyspaced points around the chain loop. The pawls of each pair areidentical, but are mounted differently as will be described. The leadingpawl 58A is a U-shaped member having side flanges 59 that are inclinedrearwardly and outwardly of the chain loop at their leading edges to acrosspiece 60. Secured to the inner sides of the side flanges 59 andalong their inner free edges are reinforcing strips 61 which projectslightly beyond the inner edges of the pawl flanges. The projectinginner edges of the reinforcing strips may be arcuately cut away as at 62for clearance in passing around the corners of the conveyor. Thetrailing edges of the side flanges 59 are generally perpendicular to theinner edges as indicated at 63. The trailing pawls generally indicatedat 64A are also inwardly concave U-shaped members having side flanges 65which extend perpendicularly along their leading edges at 66 tocrosspieces 67. The trailing edges of the side flanges are inclinedrearwa'rdly and inwardly at 68 and reinforc- 4 ing strips 69 are securedto the inner sides of the side flanges and project therebeyond in thesame manner as the reinforcing strips 61. The inner edges of the strips69 may be similarly recessed as at 70 for clearance.

The leading pawl 58A of the first pair of pawls shown at 57A in FIGURESl, 2 and 6 is secured to the chain 46 by an elongated pin 71 which formsone of the connecting pins for the adjacent links 72 of the chain. Thepawl is mounted in olf-center straddling relation to the chain 46 andlaterally outwardly therefrom toward the bar supporting track 19 by arelatively long sleeve 73 positioned between the inner side of thereinforcing plate and the outer links of the chain. A set collar 74secured to the pin at the opposite inner side of the chain keeps the pinand sleeve in position laterally relative to the chain and the inside ofthe pawl. One of the pins 75 of the chain positioned in trailingrelation to the pin 71 is longer than the normal link connecting pins 76of the chain but shorter than the pin 71 to be positioned freely betweenthe side flanges 59 of the pawl. The pin 75 is spaced from the side ofthe chain 47 and secured in place by a collar 77. As appears moreclearly from FIG. 6 the ends of the pin 75 overlie notches 78 formed inthe upper edges of the reinforcing strips 61 so that the pawl may pivotdownwardly or outwardly relative to the circuit of the conveyor but isprevented from tilting inwardly by engagement between the ends of thepin and the bottoms of the notches which form stops on the pawls.

The trailing pawl 64A of the top illustrated pair of pawls 57A isconnected to a pin 79 of the chain in trailing relation to the leadingpawl. Like the pin 71, the pin 79 projects through a sleeve or roller ofthe chain and extends through the side flanges of the trailing pawl. Thepawl is positioned in off-center straddling relation to the chain 46 ininwardly or more widely spaced relation to the track 19. This isaccomplished by a relatively long sleeve 80 positioned between the innerside of the chain and the inner flange of the pawl and held axially inplace by a lock collar 81.

A trailing pin 32 of the chain is of intermediate length similar to pin75 and is retained transversely of the chain by a lock collar 83. Pin 82registers with notches 84 in strips 69 on the inner sides of the sideflanges 65 to prevent swinging of the pawl outwardly of the chain loopwhile permitting inward swinging of the pawl.

. The leading and trailing pawls of the lower pair of pawls 57B as shownin FIGURES 1 and 10 are the same as the first pair of pawls and aresecured to the chain 46 in a similar fashion except that the leadingpawl 588 shown in FIGS. 1 and 10 is offset inwardly from the supportingtrack 26 while the trailing pawl 64B is offset oppositely and outwardlyaway from the track 26. Similar spacing sleeves 73B and 80B and lockcollars 74B and 818 secure the pins 718 and 79B in correct longitudinaland transverse relation between the chain and the pawl. Likewise theintermediate length pins 75B and 82B are held in place by set collars77B and 83 The upper pawl guiding and supporting rail 22 is providedadjacent its front end with a pair of slots or recesses 85 and 86 thatare in outwardly olf-center relation to the chain supporting rail or rib23 to receive the side flanges of outwardly offset leading pawl 64 ofthe first pair of pawls 57A and the side flanges of the outwardly offsettrailing pawl 58B of the other pair of pawls 57B as these pawls areadvanced forwardly along the top supporting rail 22. At its rear end thetop rail 22 is provided with a second pair of slots 87 and 88 which areoffset inwardly to receive the flanges of the alternate pawls of eachpair of pawls. Slots 89 in each end of the top rail provide clearancefor the sprockets 42 and 45. The bottom pawls supporting rail 29, as isshown in FIGURE 9, is provided with a pair of slots 90 and 91 adjacentits forward end which are offset laterally inwardly away from the barsupporting track 26 while the opposite or rear end of the rail isprovided with slots 92 and 93 which are offset oppositely outwardlytoward the track 26. The ends of the rail 29 have slots 94 formedtherein to clear the peripheries of the sprockets 43 and 44.

From the foregoing description of the oppositely staggered slots in thepawl support rails and the oppositely offset pawls in the two pairs ofpawls, it will be apparent that the leading pawl 58A of the upper pairof pawls 57A will register with the slots 85 and 86 and tilt downwardlytherethrough as shown in FIGURE 6 to pass underneath the articlesupporting bar 48 located in the detent 51 as the chain 46 is advancedto the left as shown in FIGURES l and 6. The ends of the slots 85 and 86will cam the pawl 58A outwardly in a position for its trailing edge 63to engage and support the bar 43 downwardly along the front support rail32 as the trailing pawl 64A pushes the bar 43 out of the detent. Thetrailing pawl 64A being offset from the chain oppositely from itsassociated leading pawl, will not enter into the slots 85 and 86 andwill push the bar and its roller forwardly out of the detent. The detent51 and the space therebelow is thus vacated. The opposite pair of pawls57B, shown at the bottom of FIGURE 1, will be moving article support bar49 rearwardly from detent 53, clearing detent 53 to receive bar 48. Whenthe trailing pawl 64B reaches detent 54- at the rear of the lowersupport rail, its outwardly offset side flanges register with slots 92and 93 to pass bar 49 as shown in FIG. 10, and leave bar 49 on detent54. Inwardly offset trailing pawl 64A will later pick up and advance bar49. The second pair of pawls 57B continues up to the top support track19 and the support bar resting in the detent 52, the leading pawl 58Bpasses under bar 50 by reason of its flanges being in registeringrelation with respect to the slots 87 and 88 but the outwardly off-setflanges of trailing pawl 648 do not register with the slots. One of thenext advancing cycles of the chain article support bar 50 in the detent52 is advanced to the then vacant front top detent 51 by trailing pawl64B where it is left by reason of the outwardly off-set position of itsside flanges registering with and falling into slots and 86.

The arrangement of the pairs of pawls 57A and 5713 in oppositely offsetstraddling relation to the chain 46 and the oppositely staggeredrelation of the slots 85 to 88 and 90 to 93 provides the same sequenceof advancing motion of the three article support bars 48, 49 and 5% asthe structure in Patent No. 2,836,303 referred to above. At the sametime the bar advancing pawls are supported on opposite sides of thechain completely around the circuit of the chain to support the loadsapplied thereto in advancing the bars. The article supporting bars orrather their rollers 47 are retained laterally on the advancing pawlsthrough the vertical reaches of the conveyor by the retaining flanges 3and 4, and the vertically moving pawls are oppositely supported by thevertical flanges 32 and 37. In passing between the vertical flanges 32and 37 and the top roller supporting track 19, the rollers 57 aresupported and guided by curved extensions 95 projecting from the ends oftrack 19. The ends of the vertical flanges 32 and 37 are slotted as at96 to clear the sprockets 42, 43, 44 and 45.

No attempt has been made to illustrate the driving connection to thechain conveyor 46 as this is disclosed in the prior patent referred to.

What is claimed as new is:

1. In an article storage and display device having conveyor chainsarranged in spaced, upright, generally rectangular loops, with pairs ofleading and trailing pawls connected to the chains in two equally spacedpositions around said loops, sprockets located in the corners of saidloops, and three article support rods extending between said loops to beadvanced by said pawls between four positions located adjacent thecorners of the loops, chain and rod guiding and pawl supportingmechanism comprising:

top and bottom chain and pawl supporting rails extending laterallyinwardly across the plane of said loops with the top rail below the topreach of the associated loop and the bottom rail above the bottom reachof the associated loop, with the chains engaged with laterally inwardlyspaced central portions of the rails,

top and bottom bar support tracks positioned in laterally overlappingrelation to the outer portions of said chain and pawl supporting railswith the top bar support track located above the top support rail andthe bottom bar support track located below the bottom pawl supportingrail,

bar restraining detents on said bar supporting tracks adjacent the endsthereof,

front and rear upright bar retaining tracks extending between the endsof said top and bottom bar supporting tracks with curved meansconnecting the upright tracks to the ends of the bottom bar,

upright front and rear chain and pawl guiding rails disposed in spacedrelation to the inner sides of said front and rear tracks and havingtheir ends spaced from the ends of said top and bottom rails,

sprockets engaging said chain loop and positioned in chain transferringrelation between the ends of the rails,

said pawls having U-shaped cross sections with side flanges projectinginwardly of said chain loop to engage said rails,

first pivot pins connecting the leading ends of said leading pawls tosaid chain in laterally opposite offcenter but straddling relation tothe outside of said chain loop,

second pivot pins connecting the leading of said trailing pawls inspaced relation behind said leading pawls and in laterally oppositeoff-center but straddling relation to the outside of said chain loopwith each trailing pawl off-set oppositely to its associated leadingpawl,

means on the insides of the side flanges of said pawls forming stopsdisplaced in trailing relation to pivot pins connected thereto, stoppins projecting from said chain in overlying relation to said stopsoutwardly of said chain loop,

first pairs of longitudinal recesses formed in said top and bottomsupport and guide rails and located near the front ends thereof toreceive the trailing'edges of the side flanges on the leading pawl ofone of said pairs and the side flanges of the trailing pawl of the otherof said pairs of pawls to permit inward tilting of the pawls to passsupport bars engaged with the detents in said front ends, and otherpairs of longitudinal recesses formed in the rear ends of said top andbottom rails in laterally oppositely off-set relation to said firstpairs of recesses to receive the trailing edges of the side flanges ofthe leading pawl of said other of said pairs of pawls and the sideflanges of the trailing pawl of said one of said pairs of pawls. 2. Astorage and display device as defined in claim 1 in which said pawls areof folded metal with opposed edges on the trailing ends of the leadingpawls and the leading edges of the trailing pawls, said edges beinggenerally perpendicular to the inner edges of the side flanges of thepawls, and

strips of metal secured to the inner sides of the side flanges of saidpawl-s and receiving said pivot pins,

said strips of metal having notches formed in their outer edges formingsaid stops for coaction with said stop pins,

said pivot pins and said stop pins projecting axially from connectingpins of said link chain.

3. A storage and display device as defined in claim 2 in which saidstrip of metal on said pawls project beyond the inner edges of the sideflanges of said pawls to form rail engaging surfaces on the pawls.

4. An article storage and display device as defined in claim 1 in whichtop and bottom chain and pawl supporting rails and said top and bottombar supporting tracks are angled sheet metal members having verticallyturned mounting flanges on their outer sides,

said front and rear guiding rails being of angled metal with mountingflanges turned parallel to the plane of said chain loop, and

front and rear upright connecting bars connected to the flanges on saidrails and said top and bottom support tracks.

5. An article storage and display device as defined in claim 4 in whichsaid front and rear upright bar retaining tracks are of angled crosssection with laterally turned parallel flanges forming their barretaining portions,

the lower ends of said laterally turned flanges being curved toward theends of said top and bottom rails to form said curved connecting means,and

top and bottom cross bars connected to said front and rear uprightconnecting bars and to said front and rear bar retaining tracks.

6. An article storage and display device as defined in claim 4 in whichsaid recess in said top and bottom pawl supporting rails are slotsformed in the sheet metal of the rails, and

chain supporting and guiding ribs secured to said rails.

7. An article storage and display device as defined in claim 4 in whichsaid pawl supporting rail and bar supporting track are integral piecesof folded metal at the top and bottom of the device.

References Cited UNITED STATES PATENTS 707,200 8 1902 Bollinger.2,836,303 5/1958 Lyon 2lll.5

' FOREIGN PATENTS 25 9,709 10/ 1926 Great Britain.

ROY D. FRA ZIER, Prim ry Examiner. R. P. SEITTER, Assistant Examiner.

1. IN AN ARTICLE STORAGE AND DISPLAY DEVICE HAVING CONVEYOR CHAINSARRANGED IN SPACED, UPRIGHT, GENERALLY RECTANGULAR LOOPS, WITH PAIRS OFLEADING AND TRAILING PAWLS CONNECTED TO THE CHAINS IN TWO EQUALLY SPACEDPOSITIONS AROUND SAID LOOPS, SPROCKETS LOCATED IN THE CORNERS OF SAIDLOOPS, AND THREE ARTICLE SUPPORT RODS EXTENDING BETWEEN SAID LOOPS TO BEADVANCED BY SAID PAWLS BETWEEN FOUR POSITIONS LOCATED ADJACENT THECORNERS OF THE LOOPS, CHAIN AND ROD GUIDING AND PAWL SUPPORTINGMECHANISM COMPRISING: TOP AND BOTTOM CHAIN AND PAWL SUPPORTING RAILSEXTENDING LATERALLY INWARDLY ACROSS THE PLANE OF SAID LOOPS WITH THE TOPRAIL BELOW THE TOP REACH OF THE ASSOCIATED LOOP AND THE BOTTOM RAILABOVE THE BOTTOM REACH OF THE ASSOCIATED LOOP, WITH THE CHAINS ENGAGEDWITH LATERALLY INWARDLY SPACED CENTRAL PORTIONS OF THE RAILS, TOP ANDBOTTOM BAR SUPPORT TRACKS POSITIONED IN LATERALLY OVERLAPPING RELATIONTO THE OUTER PORTIONS OF SAID CHAIN AND PAWL SUPPORTING RAILS WITH THETOP BAR SUPPORT TRACK LOCATED ABOVE THE TOP SUPPORT RAIL AND THE BOTTOMBAR SUPPORT TRACK LOCATED BELOW THE BOTTOM PAWL SUPPORTING RAIL, BARRESTRAINING DETENTS ON SAID BAR SUPPORTING TRACKS ADJACENT THE ENDSTHEREOF, FRONT AND REAR UPRIGHT BAR RETAINING TRACKS EXTENDING BETWEENTHE ENDS OF SAID TOP AND BOTTOM BAR SUPPORTING TRACKS WITH CURVED MEANSCONNECTING THE UPRIGHT TRACKS TO THE ENDS OF THE BOTTOM BAR, UPRIGHTFRONT AND REAR CHAIN AND PAWL GUIDING RAILS DISPOSED IN SPACED RELATIONTO THE INNER SIDES OF SAID FRONT AND REAR TRACKS AND HAVING THEIR ENDSSPACED FROM THE ENDS OF SAID TOP AND BOTTOM RAILS, SPROCKETS ENGAGINGSAID CHAIN LOOP AND POSITIONED IN CHAIN TRANSFERRING RELATION BETWEENTHE ENDS OF THE RAILS, SAID PAWLS HAVING U-SHAPED CROSS SECTIONS WITHSIDE FLANGES PROJECTING INWARDLY OF SAID CHAIN LOOP TO ENGAGE SAIDRAILS, FIRST PIVOT PINS CONNECTING THE LEADING ENDS OF SAID LEADINGPAWLS TO SAID CHAIN IN LATERALLY OPPOSITE OFFCENTER BUT STRADDINGRELATION TO THE OUTSIDE OF SAID CHAIN LOOP, SECOND PIVOT PINS CONNECTINGTHE LEADING OF SAID TRAILING PAWLS IN SPACED RELATION BEHIND SAIDLEADING PAWLS AND IN LATERALLY OPPOSITE OFF-CENTER BUT STRADDLINGRELATION TO THE OUTSIDE OF SAID CHAIN LOOP WITH EACH TRAILING PAWLOFF-SET OPPOSITELY TO ITS ASSOCIATED LEADING PAWL, MEANS ON THE INSIDESOF THE SIDE FLANGES OF SAID PAWLS FORMING STOPS DISPLACED IN TRAILINGRELATION TO PIVOT PINS CONNECTED THERETO, STOP PINS PROJECTING FROM SAIDCHAIN IN OVERLYING RELATION TO SAID STOPS OUTWARDLY OF SAID CHAIN LOOP,FIRST PAIRS OF LONGITUDINAL RECESSES FORMED IN SAID TOP AND BOTTOMSUPPORT AND GUIDE RAILS AND LOCATED NEAR THE FRONT ENDS THEREOF TORECEIVE THE TRAILING EDGES OF THE SIDE FLANGES ON THE LEADING PAWL OFONE OF SAID PAIRS AND THE SIDE FLANGES OF THE TRAILING PAWL OF THE OTHEROF SAID PAIRS OF PAWLS TO PERMIT INWARD TILTING OF THE PAWLS TO PASSSUPPORT BARS ENGAGED WITH THE DETENTS IN SAID FRONT ENDS, AND OTHERPAIRS OF LONGITUDINAL RECESSES FORMED IN THE REAR ENDS OF SAID TOP ANDBOTTOM RAILS IN LATERALLY OPPOSITELY OFF-SET RELATION TO SAID FIRSTPAIRS OF RECESSES TO RECEIVE THE TRAILING EDGES OF THE SIDE FLANGES OFTHE LEADING PAWL OF SAID OTHER OF SAID PAIRS OF PAWLS AND THE SIDEFLANGES OF THE TRAILING PAWL OF SAID ONE OF SAID PAIRS OF PAWLS.